An investigation is in progress of the effects of chronic hypothalamic stimulation in conscious, unrestrained squirrel monkeys on the induction and progression of atherosclerosis. Biochemical changes in plasma lipids and other parameters are correlated with morphologic alterations in major arteries. Interaction of hypothalamic stimulation with hyperlipidemia induced by atherogenic diets and hypertension induced by standardized experimental techniques are included in the investigation. In addition to the study of the role of the central nervous system in the initiation and progression of vascular lesions, the investigation focuses on some mechanisms involved by which neurally excited tissue may be associated with vascular damage.